The way I always switched between debug and release in Xcode, for my whole developer life, was like this: click on the scheme, Edit scheme…, Run, Info Build configuration. It’s exactly four clicks that take me about 5 seconds. This works fine.
It also works for the “Build all” scheme so if you want to build all formats (VST, AAX, …) at once you do not have to switch debug/release for all of their schemes, just the “Build all” one.
If you want your custom scheme to have even less clicks, then yes you have to create it yourself. And yes, any such custom scheme will be overwritten next time you save the project from the Projucer. The reason is that in JUCE 4.2, the Projucer needs to create multiple targets for your audio plug-in, and for every new target Xcode will generate a new scheme.
I believe there is another way of “saving” your custom schemes and re-applying them after you re-saved the project, something involving exporting and importing schemes. Maybe that would be useful. Unfortunately I don’t know how it works, but Fabian does. He will be back on Monday, I’ll ask him to post this here.
Hope this is helpful,